As a conventional damping valve, for example, there is a known piston valve provided in a piston portion of a damper for a vehicle. The piston valve has an annular leaf valve laminated on an outlet end of a port which is provided in the piston portion, and the port is opened and closed by this leaf valve.
In the above piston valve, by fixing and supporting the inner circumferential side of the leaf valve and warping the outer circumferential side, the port is opened and closed by the leaf valve. When warping rigidity of the leaf valve is reduced, a damping force in a low speed region of piston speed is excessively decreased, and when the warping rigidity is increased, a damping force in a mid-high speed region of the piston speed is excessively increased. Thus, ride quality in the vehicle is not easily satisfied in all the speed regions.
Therefore, JP9-291961A discloses a valve structure in which the inner circumferential side of a leaf valve is not fixedly supported, the leaf valve is slidably installed to an outer circumference of a tubular piston nut attached to a leading end of a piston rod, and this leaf valve is biased by a coil spring.
In a damper to which this valve structure is applied, when piston speed at the time of an extension operation of a piston is in a low speed region, the leaf valve is not opened but a damping force is generated only by an orifice engraved on a valve seat. Thus, the damper exerts the same damping characteristic as a valve structure in which an inner circumference is fixedly supported.
On the other hand, when the piston speed of the damper reaches a mid-high speed region, a pressure of working oil passing through a port is applied to the leaf valve, and the leaf valve is warped and opened. Thereby, against a bias force of the coil spring, the leaf valve is lifted in the axial direction from the piston and retreated together with a main valve. Thus, in comparison to the valve structure in which the inner circumference is fixedly supported, a flow passage area is increased. Therefore, an excessive increase in the damping force with the piston speed of the mid-high speed region is prevented, so that the ride quality in the vehicle can be satisfied in all the speed regions at the time of the extension operation.